The present invention relates to new ceramics possessing electroconductivity and low thermally expansive property.
Known hitherto as electroconductive ceramics are porous ceramics obtained by adding a metal fluoride to a metal diborate or a mixture of a metal diborate and a metal disilicide and sintering the resultant mixture, silicon carbide, lanthanum chromite and zirconia and the like.
However, these known electroconductive ceramics have many drawbacks. As these ceramics show a non-linear change in electroconductivity to temperatures, thus limiting the range of applicable temperatures. Because of high thermal expansibility, these ceramics have poor thermal impact-resistance and tend to crack by rapid change of temperature. In addition, these ceramics are porous and have low mechanical strength.
As a result of various researches made for overcoming the drawbacks of these known electroconductive ceramics and for developing new type electroconductive ceramics possessing a low thermal expansion coefficient and a dense structure, it has now been found that this purpose can be attained by properly combining low thermally expansive or negatively thermally expansive ceramics with an electroconductive substance. The present invention is based on the above finding.